Process for raising the melting point of acetone-soluble copolymers



nited States Patent PROCESS FOR RAISING THE MELTING POINT OFACETONE-SOLUBLE COPOLYMERS y Marshall W. Duke and David A. Gordon,Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Application July 11, 195.6 SerialNo. 597,091

8 Claims, .(Cl. 260--85.5)

This invention relates to a novel process for raising the melting pointof certain acetone-soluble copolymers.

More particularly it relates to such a process for raising the meltingpoint of acetone-soluble copolymers composed of vinylidene chloride andacrylonitrile.

In U. S. 2,681,325 are disclosed certain copolymers of vinylidenechloride and acrylonitrile which are solublein acetone in concentrationsnecessary for spinning continuous fibers and filaments and for castingcontinuous films. Those copolymers contain from 30 to 55 percentacrylonitrile and correspondingly from 70 to 45 percent vinylidenechloride. The acetone spinning dopes prepared with those polymers couldbe" spun by either wet or dry spinning techniques, and the fiberssoprepared were found to have an interesting family of properties forcommercial use. 'Tho'se fibers had one serious drawback, however. Theyhad a softening range or melting point that was so low that the fabricwoven from the fibers could not be ironed. Attempts were made to raisethe melting point of the fibers by increasing the molecular weight ofthe copolymer. Other attempts involved the preparation of a morehomogeneous copolymer by special polymerization techniques. Thoseattempts as well as all others either failed to raise the melting pointof the fibers or destroyed the acetone solubility of the copolymer. Itwould be desirable to have a process for preparing acetone-solublecopolymers composed of vinylidene chloride and acrylonitrile havinghigher melting points than the prior copolymers and the provision ofsuch a process is the principal object of this invention.

Other objects will be apparent as the description of the inventionproceeds.

It has now been found that the melting point of articles prepared fromacetone soluble copolymers of vinylidene chloride and acrylonitrile israised by preparing an acetone dope comprising the copolymer, and anacetone soluble acetylenic diol and fabricating the dope into an articlewhich is substantially acetone free.

The copolymers useful in the process of this invention are thosedescribed in U. S. 2,681,325 as containing from 30 to 55 percent byweight of acrylonitrile and correspondingly from 70 to 45 percent byweight of vinylidene chloride. Optimum results are obtained when thecopolymer is one of 40 percent by weight of acrylonitrile and 60 percentvinylidene chloride. For use in continuous articles such as fibers andfilms the copolymers should have a molecular weight which would give asolution viscosity of at least 1.5 centipoises and not to exceed 2.5centipoises when measured from a solution of 0.5 gram of the copolymerdissolved in 100 milliliters of dimethyl formamide at 25 C. Preferablythe viscosity as thus measured should be between 1.8 to 2.2 centipoises.

Typical examples of useful acetylenic diols in the process of thisinvention include dimethyl hexynediol, dimethyloctynediol,2,5-diphenyl-3-hexyne-2,5-diol, and 2,7dimethylocta-3,5-diyne-2,7-diol.

' acetone.

2,878,238 Patented Mar. 17, 1959 For casting films and spinning fibersit is desirable to have a solution of from 1 0. to 20 percent by weightof the defined copolymer in acetone, and solutions of that concentrationrange may be easily prepared by stirring the polymer into the acetone atroom temperature, Less stirring is needed when the acetone is warmed to35 to 45 C. Following dissolution of the, copolymer in the acetone theacetylenic diol may be dissolved in the dope. The order of dissolutionof the copolymer and modifier is not critical, and, if desired, theacetylenic diol maybe dissolved first, followed by the copolymer, or thedis solution of the ingredients may be carried out simultaneously.

To achieve the stated objective of the process of this invention ofraising the melting point of the article, the acetylenic diol should beemployed in an amount of from 1 to 5 percent of the weight of thecopolymer. When less than 1 percent is used there is very little if anyelevation of the melting point, while the use of more than 5 percent cancause insolubility of the product.

Following preparation of the dope, a continuous article is fabricatedbycasting a film or by wet or dry spinning fibers. The articles are thenair dried or subjected to moderate temperatures to remove any readilyvolatile matter, after which the articles are subjected to an elevatedtemperature for a short time to cause chemical reaction between thecopolymer and the acetylenic diol and to fuse or to sin'ter the article.Forexample, exposure of an article to a temperature of about ;"-=C. forabout 15 minutes will suffice. Temperatures of 150 to 200 C. are mostusefuL' :Wh en the'articles are exposed to such temperatures forprolonged periods the products become insoluble.

The inventors believe that the elevation in melting point without lossof acetone solubility is due principally to a minor amount ofcross-linking of the copolymer chains. Fibers, fabrics and filmsproduced in accordance with this process are capable of being ironed atthe usual temperatures used for ironing synthetic fibers and the fabricsproduced therefrom. If desired, an acetone insoluble product may beprepared by using greater than the stated amounts of modifier andsubjecting the formed article to elevated temperatures for prolongedperiods.

By way of illustration, several dopes were prepared from 240 parts byweight of anhydrous acetone, 57 parts by weight of a copolymer composedof 60 percent vinylidene chloride and 40 percent acrylonitrile, and 3parts by weight of several acetylenic diols. For comparative purposes,one dope had no acetylenic diol compound. Each of the dopes was castonto a stainless steel plate to a dry thickness of 0.0025 inch. The wetcast films were air dried for 24 hours followed by an oven drying forone hour at 55 C. to remove substantially all of the The dried filmswere then heated at 150 C. for up to 60 minutes after which strips ofthe films A1 inch wide were cut for determining an apparent meltingpoint and solubility. The apparent melting point is a melting pointunder a low load, and often provides a sharp point for many polymericmaterials which soften over a range of temperatures and show no truemelting point. The determination was made by weighting one end of thefilm strip equivalent to 1400 gms./cm. of cross-section. The other endof the strip was clamped so that the weighted end hung free. A variableresistance cylindrical heating element was placed so as to contact about0.5 inch of the film. The heating element was brought to C. beforemounting the strip. The temperature was then raised until the film stripeither melted and broke or until 300 C. was reached. If the film had notmelted at 300 C. it was considered to have been adequately cross-linked.

-Acetone solubility-was determinedby immersing the strips in acetone forone hour at room temperature. The strips were then examined visually andrated arbitrarily as 'solubleypartially soluble, and-insoluble.

It can be seen that the melting points of the films prepared inaccordance with this invention are at least 100 0. higher than the blankwhich contained no agent.

when the heatstability of the film strips was compared it was found thatthe strips of this invention were at least as stable as the blank, i.e., they showed no more,

and often less evidence of discoloration after prolonged thermalexposure.

The invention has been illustrated by tests carried out on film strips.It is equally applicable to the improvement in thermal properties offilamentary products made ,from the acetone solutions of the copolymersand acetylenic diols.

. We claim:

1. A. process for increasing the melting point of acetone-solublecopolymers of vinylidene chloride without destroying acetone solubilitycomprising sequentially preparing an acetone solution of a copolymercomposed of from 30 to percent by weight of acrylonitrile andcorrespondingly from to 45 percent by weight of vinylidene chloride andfrom 1 to 5 percent of the weight of said copolymer of anacetone-soluble acetylenic diol, removing acetone from the solution, andfinally subjecting the acetone-free composition to an elevatedtemperature for at least about 15 minutes and until the melting point-of the copolymer has beenraised.

2. The process claimed in claim 1,'wherein said acetone solutioncontains from 10 to 20 percent by weight of said copolymer.

3. The process claimed in claim 1, wherein said copolymer is composed of40 percent by weight of acry lonitrile and 60 percent by weight ofvinylidene chloride.

4. The process claimed in claim 1, wherein said elevated temperature isat least C.

5. The process claimed in claim 1, wherein the solution of copolymer andacetylenic .diol is spun in filamentary form and'the resulting productis freed from acetone and heated to a temperature of 150 to 200 C.

6. The process claimed in claim 1, wherein said acetylenic diol isdimethylhexynediol.

7. The process claimed in claim 1, wherein said acetylenic diol is2,5-diphenyl-3-hexyne-2,5-diol.

8. The process claimed in claim 1, wherein said acetylenic diol is2,7-dimethylocta-3,5-diyne-2,7-diol.

References Cited in the file of this patent UNITED STATES PATENTS2,681,325 Abernathy June 15, 1954

1. A PROCESS FOR INCREASING THE MELTING POINT OF ACETONE-SOLUBLECOPOLYMERS OF VINYLIDENE CHLORIDE WITHOUT DESTROYING ACETONE SOLUBILITYCOMPRISING SEQUENTIALLY PREPARING AN ACETONE SOLUTION OF A COPOLYMERCOMPOSED OF FROM 30 TO 55 PERCENT BY WEIGHT OF ACRYLONITRILE ANDCORRESPONDINGLY FROM 70 TO 45 PERCENT BY WEIGHT OF VINYLIDENE CHLORIDEAND FROM 1 TO 5 PERCENT OF THE WEIGHT OF SAID COPOLYMER OF ANACETONE-SOLUBLE ACETYLENIC DIOL, REMOVING ACETONE FROM THE SOLUTION, ANDFINALLY SUBJECTING THE ACETONE-FREE COMPOSITION TO AN ELEVATEDTEMPERATURE FOR AT LEAST ABOUT 15 MINUTES AND UNTIL THE MELTING POINT OFTHE COPOLYMER HAS BEEN RAISED.